Sensorless force control for transesophageal echocardiography probe

ABSTRACT

A robotic actuation system for sensorless force control of an interventional tool ( 14 ) having cable driven distal end (e.g., a probe, a steerable catheter, a guidewire and a colonoscope). The system employs a robotic actuator ( 30 ) having one or more motorized gears operate the cable drive of the interventional tool ( 14 ). The system further employs a robotic workstation ( 20 ) to generate motor commands for simultaneous actuation position and contact force control of the interventional tool ( 14 ). The motor commands are a function of an actuation position measurement and a motor current measurement of the at least one motorized gear for a desired actuation position of the interventional tool ( 14 ).

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a continuation application of Ser. No. 15/112,707,filed Jul. 20, 2016, which is the U.S. National Phase application under35 U.S.C. § 371 of International Application No. PCT/IB2015/050302,filed on Jan. 15, 2015, which claims the benefit of U.S. ProvisionalPatent Application No. 61/931,203, filed on Jan. 24, 2014. Theseapplications are hereby incorporated by reference herein.

The present invention generally relates to transeesophagealechocardiography (“TEE”) probes. The present invention specificallyrelates to sensorless force control of the TEE probe during aninterventional procedure.

Transeesophageal echocardiography is commonly used to visualize cardiacanatomy and interventional devices during treatment for structural heartdisease (“SHD”). FIG. 1 shows a typical distribution of theatre staffwithin a lab room 10 having an ultrasound workstation 11 and an x-rayscanner, of which a c-arm 12 is shown. During a KID operation, anechocardiographer 13 holds a TEE probe 14, which passes through a mouthof a patient 16 into an esophagus to visualize a heart of patient 16. Acardiologist 15 is located on an opposite side of x-ray c-arm 12 and anoperating table 17. Cardiologist 15 navigates interventional devices(not shown) (e.g., catheters and guidewires) from arterial incisionsinto the heart under x-ray guidance and ultrasound guidance via TEEprobe 14 in order to perform different diagnostic or therapeuticprocedures. Exemplar procedures, such as mitral clip deployments ortranscatheter aortic valve replacements (“TAVR”), can be time consumingand complex. Moreover, ensuring appropriate visualization of the targetanatomy during the procedure is the responsibility of echocardiographer13, who must make constant small adjustments to a position of a tip ofTEE probe 14 for the duration of the procedure.

In practice, the operating conditions of FIG. 1 present severalchallenges. The first challenge is fatigue and poor visualization.Specifically, appropriate visualization includes both ensuring therelevant anatomical structures are within the field of view, and thatthe necessary contact force between the transducer head and esophagealwall, to achieve adequate acoustic coupling, is achieved. To this end, aposition and an orientation of a head of TEE probe 14 requires constant,minute adjustments for the duration of the procedure in order tomaintain appropriate visualization of the target structures. This canlead to fatigue and poor visualization by echocardiographer 13 duringlong procedures.

The second challenge is x-ray exposure. Specifically, a length of TEEprobe 14 results in the positioning of echocardiographer 13 in closeproximity to the source of interventional x-ray system, thus maximizingthe x-ray exposure of echocardiographer 13 over the course of theprocedure.

The third challenge is communication and visualization. During certainphases of a procedure, cardiologist 15 and echocardiographer 13 must bein constant communication as cardiologist 15 instructs echocardiographer13 as to which structure to visualize. Given the difficultlyinterpreting a 3D ultrasound volume, and the different co-ordinatesystems displayed by the x-ray and ultrasound systems, it can bechallenging for echocardiographer 13 to understand the intentions ofcardiologist 15.

The present invention provides a robotic actuation system to addressthese challenges. Generally, as shown in FIG. 2, a new distribution oftheatre staff within a lab room 10 b with the robotic actuator systememploying a robotic workstation 20 and robotic actuator 30 for remotecontrol of between two (2) degrees of freedom and (4) degrees of freedomof TEE probe 14 which adjust the ultrasound imaging volume of TEE probe14. Additionally, as will be further described herein, robotic actuator30 may have the ability to be retrofitted to existing and various typesof TEE probe 14 and may have the ability to be rapidly remove from TEEprobe 14 should echocardiographer 13 decide to return to manualoperation of TEE probe 14 for any reason.

A potential issue however arising from robotic control of TEE probe 14is safety. Specifically, as the dials of TEE probe 14 are moved by rotoractuator 30 and not by hand of echocardiographer 13, then there is nohaptic feedback (i.e., echocardiographer 13 cannot feel if the probe 14is exerting excessive forces on the esophagus of patient 16).

Force control of robots is known in art in applications such as grindingor assembly. These methods use force sensors to detect force or torqueon the robot end-effector or in the robot joints. Similarly,probe-tissue contact force may be measured with force sensors known inart. However, there are several issues with measuring probe-tissuecontact force with force sensors.

First, TEE probe 14 has to be modified to include the force sensors. Forsafety and comfort of patient 16, the size of TEE probe 14 has to be assmall as possible. Conversely, for guidance and diagnostic purposes, theimaging element of TEE probe 14 has to be as large as possible toincrease the field-of-view. With these constraints, adding newelectronics to the head of TEE probe 14 may interfere with the mainfunction of TEE probe 14, which is the acquisition of ultrasound images.

Second, the sensors can only be placed at discrete locations of TEEprobe 14, whereas an injury to patient 16 may occur at any point along alength of the entire TEE probe 14.

Third, if direct force sensing is used, then any force sensor basedcontrol system may only be used with the newly manufactured probes only.However, it would be beneficial to use a force control system with TEEprobes 14 already deployed in the field.

Sensor-less force control is also known in art where the force isinferred from other parameters of the system, most typically current inthe motors. In traditional robotic applications, the force and positionare decoupled. In these applications, the control scheme combines pathcontrol and force control. For example, the path control loop cancontrol the process in non-compliant mode while the force control loopcan control the system in the compliant mode. These dual loops can alsorun concurrently. Furthermore, in traditional robotic applications, thecurrent in the motor of end-effector does not depend on the position ofthe entire robot which simplifies sensor-less force control.

The problem of force-control of TEE probe 14 is unique to the family ofdevices that are cable-driven (e.g., TEE ultrasound probes andcatheters) because the entire actuation is done at the proximal end ofTEE probe 14 leading to a couple of issues. First, forces sensed ormeasured in the motors of robotic actuator 30 will depend on the forcethe TEE probe 14 is exerting on the tissues as well as on the shape ofthe entire length of TEE probe 14. Second, force sensed or measured inmotors of robotic actuator 30 includes force needed to pull cables. Thisforce will vary depending on position of the head of TEE probe 14.

The present invention provides sensor-less force control of TEE probe 14by robotic workstation 20 processing a simultaneous tip position/forceestimate of TEE probe 14 from robotic actuator 30. This allows a saferemote manipulation of TEE probe 14, thereby reducing the risk of injuryto an esophagus of patient 16, and allows robotic workstation 20 androbotic actuator 30 to be utilized with the probes already deployed inthe field.

One form of the present invention is a robotic actuation system forsensorless force control of an interventional tool having a cable drivendistal end (e.g., a probe, a steerable catheter, a guidewire and acolonoscope). The system employs a robotic actuator having one or moremotorized gears to operate the cable drive of the interventional tool.The system further employs a robotic workstation to generate motorcommands for simultaneous actuation position and contact force controlof the interventional tool. The motor commands are a function of anactuation position measurement and a motor current measurement of the atleast one motorized gear for a desired actuation position of theinterventional tool.

The foregoing form and other forms of the present invention as well asvarious features and advantages of the present invention will becomefurther apparent from the following detailed description of variousembodiments of the present invention read in conjunction with theaccompanying drawings. The detailed description and drawings are merelyillustrative of the present invention rather than limiting, the scope ofthe present invention being defined by the appended claims andequivalents thereof.

FIG. 1 illustrates an exemplary manual actuation of a TEE probe as knownin the art.

FIG. 2 illustrates an exemplary embodiment of a remote controlledactuation of a TEE probe in accordance with the present invention.

FIG. 3 illustrates an exemplary TEE probe as known in the art.

FIGS. 4A and 4B illustrate exemplary engagements of an actuation dial ofthe TEE probe shown in FIG. 3 and a motorized gear in accordance withthe present invention.

FIG. 5 illustrates an exemplary embodiment of a robotic actuator inaccordance with the present invention.

FIGS. 6A and 6B respectively illustrate exemplary embodiments of a probehandle base and a probe handle cover in accordance with the presentinvention.

FIG. 7 illustrates a schematic embodiment of the probe handle base andthe probe handle cover shown in FIGS. 6A and 6B in accordance with thepresent invention.

FIGS. 8A and 8B illustrate an exemplary embodiment of an actuatorplatform in accordance with the present invention.

FIGS. 9A-9D illustrate an operation of the actuator platform shown inFIGS. 8A and 8B.

FIG. 10 illustrates an exemplary embodiment of a robotic workstation inaccordance with the present invention.

FIG. 11 illustrates a flowchart representative of an exemplaryembodiment of an actuation position calibration method in accordancewith the present invention.

FIG. 12 illustrates a flowchart representative of an exemplaryembodiment of a contact force calibration method in accordance with thepresent invention.

FIG. 13 illustrates an exemplary embodiment of a sensorless forcecontrol in accordance with the present invention.

To facilitate an understanding of the present invention, exemplaryembodiments of a robotic actuation system of the present invention andvarious components therefore will now be described in the context of aremote control actuation of a TEE probe as shown in FIG. 3. From thesedescriptions, those having ordinary skill in the art will appreciate howto apply the principles of a robotic actuation system of the presentinvention to any suitable designs of ultrasound probes for any type ofprocedure as well as other tendon driven flexible devices (e.g.,colonoscope, gastroscope, etc.).

Referring to FIG. 3, a TEE probe 40 as known in the art employs a handle41 and an elongated probe having a proximal end 42 p attached to handle41 and a distal head end 42 d with an ultrasound transducer 45. TEEprobe 40 employs a yaw actuation dial 43 for adjusting a yaw degreefreedom of probe head 42 d, and a pitch actuation dial 44 for adjustinga pitch degree freedom of probe head 42 d.

The present invention provides gears that are motorized to control anactuation of yaw actuation dial 43 and pitch actuation dial 44. Forexample, as shown in FIG. 4A, a friction gear 31 of the presentinvention is designed to frictionally engage with yaw actuation dial 43to transmit sufficient torque for controlling a rotation of yawactuation dial 43. By further example, as shown in FIG. 4B, a crownedgear 32 of the present invention is designed to mechanically engage withpitch actuation dial 44, without contacting yaw actuation dial 43, forcontrolling a rotation of pitch actuation dial 44.

While in practice a design of a gear of robotic actuator 30 (FIG. 2)will be dependent upon a design of a corresponding actuation dial of aprobe intended to be engaged thereby, embodiments of robotic actuator 30will be described herein in the context of gears 31 and 32.

Referring to FIG. 5, one embodiment of robotic actuator 30 employs aprobe handle cover 33 having a concave inner surface 33 a and a probehandle base 34 having a concave inner surface 34 a for defining aactuation chamber upon being magnetically coupled via one or moremagnetic couplers, such as, for example, magnetic couplers 37 a and 37 bas shown. In operation, the chamber houses the actuation dials of theprobe and the magnetic coupling provides an advantage of facilitating aneasy removal of the probe if desired, particularly if operatingcircumstances dictate manual control of the probe.

Robotic actuator 30 further employs a motor 35 a and a motor controller36 a (“MCONTROLLER”) for gear 31 and a motor 35 b and a motorcontrollers 36 b for gear 32, which yields motorized gears controllableby robotic workstation 20 (FIG. 2) via an electrical coupling of roboticworkstation 20 to motor controllers 36 a and 36 b. In operation, themotorized gears are sufficient to engage and rotate the actuation dialsof the probe, which facilitates a lightweight design of probe handlecover 33.

Additionally, depending upon the environment within robotic actuator 30is being operated (e.g., an operating room), probe handle base 34 and/oran actuator platform 38 as known in the art may be utilized to securerobotic actuator 30 to a frame of reference within the environment. Forexample, probe handle base 34 and/or an actuator platform 38 may bemounted to a fixture, an operating table, operating equipment orotherwise any object for securing robotic actuator 30 to a frame ofreference within the operating room.

Referring to FIGS. 6A and 6B, a schematic embodiment of robotic actuator30 employs a probe handle base 50 and a probe handle cover 60 forcontrolling the actuation dials of a probe (e.g., probe handle 41 asshown). Specifically, probe handle cover 50 has a concave inner surface51 and probe handle base 60 has a concave inner surface 61 for definingan actuation chamber upon being magnetically coupled via magneticcouplers 52 a and 52 b of probe handle base 50 and steel locator pins 62a and 62 b of probe handle cover 60.

Probe handle base 50 employs motor control boards 53 electricallyconnected to robotic workstation 20 (FIG. 2), and probe handle cover 60employs motor control boards 63 electrically connected to motors 64(e.g., brushed DC motors via two (2) spur gears). Motor control boards53 and 63 having electrical contacts (not shown)(e.g., spring contacts)that are engaged upon a magnetic coupling of probe handle base 50 andprobe handle cover 60 to form motor controllers. Motor controller 53a/63 a implements a current control of motor 64 a to a crowned gear 65to thereby control a rotation of crowned gear 65. Similarly, motorcontroller 53 b/63 b implements a current control of motor 64 b to afriction gear 66 concentric with crowned gear 65 to thereby control arotation of friction gear 66.

FIG. 7 illustrates an aesthetic practical view of a robotic actuator 130having a magnetic coupling of a probe handle base 150 and a probe handlecover 160 for housing and controlling actuation dials (not shown) of aprobe handle 140.

FIGS. 8A and 8B illustrate one embodiment 70 of actuator platform 38(FIG. 5) employing a pair of rails 71 a and 71 b, a pair of sliders 72 aand 72 b, a pair of rotation motors 73 a and 73 b, and a crank shaft 75.By techniques known in the art, sliders 72 a and 72 b are slidablycoupled to respective rails 71 a and 71 b and affixed to respectiverotation motors 73 a and 73 b, and crank shaft 75 is rotatably coupledto rotation motors 73 a and 73 b. In operation, a platform controller 76employs hardware, software, firmware and/or circuitry for laterallymoving crank shaft 75 via conventional control of a sliding of sliders72 a and 72 b along respective rails 71 a and 71 b in one of the arrowdirections and for revolving crank shaft 75 about a rotational axis RAvia a control of rotation motors 73 a and 73 b (e.g., 180° revolution asshown in FIG. 8B). In practice, rotation motors 73 a and 73 b may haverespective groves 74 a and 74 b for supporting a portion of the probehandle, the probe itself, and/or cabling of the probe.

The importance of crank shaft 75 is to maintain a rotational alignmentof the probe handle with rotation axis RA as crank shaft 75 is laterallymoved as exemplary shown by the arrows in FIGS. 9A and 9B, or isrevolved around rotational axis RA as shown in FIGS. 9C and 9D.Specifically, crank shaft 75 extends through probe handle (“PH”) base 50and probe handle 41 as seated between probe handle base 50 and probehandle cover 60 is rotationally aligned with rotational axis RA. Assuch, lateral movement of crank shaft 75 via control of laterallysliding sliders 72 a and 72 b on respective rails 71 a and 71 b willlaterally move probe handle 40 in rotationally alignment with rotationalaxis RA as exemplary shown in FIGS. 9A and 9B. Furthermore, revolvingmotion of crank shaft around rotational axis RA via control of rotationmotors 73 a and 73 b will rotate probe handle 40 about rotational axisRA as exemplary shown in FIGS. 9C and 9D.

In practice, actuator platform 70 as shown in FIG. 7 provides anadditional two (2) degrees for freedom of lateral motion and rotationalmotion for a distal head 42 d of probe 40 capable of being pitchedand/or yawed.

Referring back to FIG. 1, robotic workstation 20 is structurallyconfigured with hardware, software, firmware and/or circuitry as knownin the art for executing technique(s) to generate motor commands to themotorized gear of robotic actuator 30 via user input. In practice,robotic workstation 20 may implement any known technique(s) forgenerating motor commands for a particular actuation scheme of a subjectprobe. More particularly to TEE probe 14, robotic workstation 20executes known technique(s) for generating the motor commands to controla pitch degree of freedom and a yaw degree of freedom of a distal headof probe 14. Additionally, if actuator platform 70 or any other actuatorplatform facilitating lateral motion and rotational motion of the distalhead of probe 14, the controller of the actuator platform may be astand-alone controller, coupled to robotic workstation 20 orincorporated within robotic workstation 20. When the controller of theactuator platform is coupled to or incorporated within roboticworkstation 20, robotic workstation 20 is structurally configured withhardware, software, firmware and/or circuitry as known in the art forexecuting known technique(s) to generate motion commands to thecontroller of the actuator platform via user input.

Also in practice, robotic workstation 20 may implement knowncomponent(s) and scheme(s) for interfacing with one or more users of therobotic actuation system. More particularly to FIG. 1, in a directcontrol scheme, robotic workstation 20 employs appropriate userinterfaces (not shown) (e.g., joystick, mouse, touch-screen, etc.) forfacilitating direct control of the head of TEE probe 14 byechocardiographer 13. In a collaborative control scheme, roboticworkstation 20 employs appropriate user interfaces (not shown) (e.g.,joystick, mouse, touch-screen, etc.) for facilitating shared control ofthe head of TEE probe 14 by echocardiographer 13 and cardiologist 15.

Referring to FIG. 10, robotic workstation 20 is structurally configuredwith hardware, software, firmware and/or circuitry in accordance withthe present invention for generating motor commands to robotic actuator30 (FIG. 2) for controlling an actuation of TEE probe 14 (FIG. 2) foracquiring ultrasound images 11 a. In practice, robotic workstation 20may execute any technique(s) suitable for the generation of such motorcommands.

In one embodiment, robotic workstation 30 employs a network 21 ofmodules 22-24 installed therein for incorporating a sensorless forcecontrol scheme of the present invention involving (1) probe calibrationmethods to establish an operational relationship between aposition/shape of a head of TEE probe 14 and motor currents of roboticactuator 30 and (2) a simultaneous actuation position and force contactof the TEE probe 14. Of importance is the one-to-one correspondence ofangular positions of gears 31 and 32 to angular positions of respectiveactuation dials 42 and 43 as exemplary shown in FIGS. 4A and 4B.

Referring to FIG. 11, a flowchart 80 represents an actuation positioncalibration method of the present invention executed by an actuationposition calibrator 22 (FIG. 10). A stage S82 of flowchart 80encompasses calibrator 22 initiating a probe actuation cycle of TEEprobe 14 by robotic actuator 30 and a stage S84 of flowchart 80encompasses a measurement of motor current by robotic actuator 30 thatis communicated to calibrator 22.

Specifically, for stage S82, TEE probe 14 may be positioned in aplurality of configurations, of which two (2) possible shapeconfigurations 90 and 91 are shown. Specifically, configuration 90entails TEE probe 14 being mounted parallel to an operating table (notshown) or configuration 91 entails TEE probe 14 being mountedperpendicular to the operating table. For either configuration, TEEprobe 14 is allowed to move freely whereby there is no additional forceexerted on the head of TEE probe 14, which keeps the head straight.

The probe calibration cycle involves robotic actuator 30 moving the headof TEE probe 14 over a full degree range of a first degree of freedomfor numerous degrees of a second degree of freedom at specified degreesample rate(s). As related to TEE probe 14, robotic actuator 30 rotatesthe yaw actuation dial over a full range of angular positions fornumerous angular positions of the pitch actuation dial at a specifiedsample rate. For example, at a calibration sampling rate of five (5)degrees and a full range of −90 degrees to 90 degrees, robotic actuator30 rotates yaw actuation dial every five (5) degrees over the full rangefor each fifth degree of angular position of the pitch actuation dial.

Each sampling involves a measurement and storage of motor current ofeach motor of robotic actuator 30. To facilitate the sensorless forcecontrol, stage S84 may entail a generation of a lookup table of themeasured motor currents. The following TABLE is an exemplary lookuptable for 649 entries derived from a range of motion){circumflex over( )}2/(sampling rate){circumflex over ( )}2+1 number of elements (pleasenote only ten (10) selected entries are shown):

PITCH YAW MOTOR PITCH MOTOR YAW DIAL DIAL CURRENT CURRENT (DEGREES)(DEGREES) (mA) (mA) −90 −90 256 195 . . . . . . . . . . . . 0 0 0 0 5 087 0 10 0 96 0 . . . . . . . . . . . . 0 5 0 43 0 10 0 65 . . . . . . .. . . . . 5 5 93 55 10 5 108 59 . . . . . . . . . . . . 90 85 254 202 9090 259 203

Calibrator 22 loops through stage S82/S84 until the end of the probeactuation cycle.

Referring to FIG. 12, a flowchart 100 represents a contact forcecalibration method of the present invention executed by contact forcecalibrator 23 (FIG. 10). A stage S102 of flowchart 100 encompassescalibrator 23 initiating a probe actuation cycle of TEE probe 14 byrobotic actuator 30 as previously described herein for stage S82 offlowchart 80 (FIG. 11) and a stage S104 of flowchart 100 encompasses ameasurement of force by a force sensor that is communicated tocalibrator 23, which in turns generates a force/motor current ratio.

Specifically, for stage S102, the head of TEE probe 14 is attached totwo (2) force sensors through two (2) springs of known mechanicalproperties. One force sensor is attached perpendicular to the probehead, such as for example, a force sensor 102 attached perpendicular tothe head of TEE probe 14 as shown in FIG. 12. The other force sensor(not shown) is attached in plane with the probe head. The springs areconfigured so that the force is zero when the probe head has a straightconfiguration 110 and is nonzero when the probe head has a bentconfiguration (e.g., bent configuration 111).

Values for motor currents and force are recorded during stage S104. Itis expected that the current force values will form a hysteresis curvefor each degree-of-freedom, which allows a line to be fitted to thesevalues to ensure that there is one force/motor current ratio accuratefor facilitating a contact force control as subsequently explainedherein.

Calibrator 23 loops through stage S102/S104 until the end of the probeactuation cycle.

Referring to FIG. 13, an actuation controller 24 (FIG. 10) implements acontrol scheme 120 of a simultaneous actuation position and contactforce control. Basically, a desired actuation position P_(D) of the headof TEE probe 14 is communicated to controller 24 by a user of roboticworkstation 20 via a joystick, keyboard or any other input device toposition control, which in response thereto controller 24 during aposition control stage S122 generates an actuation position P_(A) forTEE probe 14 in terms of a specific pitch and/or yaw of the head of TEEprobe 14 achieved by corresponding angular positions of thegears/actuation dials. Additionally, a desired force F_(D) of TEE probe14, which is typically a constant value greater than zero to maintaincontact with tissue and ensure acoustic coupling, is communicated tocontroller 24 during a force control stage S124 whereby controller 24generates a contact force correction F_(C) for actuation position P_(A)for TEE probe 14.

The generation of motor commands MC involves an application of contactforce correction F_(C) to actuation position P_(A) in view of minimizinga position error between actuation position PA and measured motorpositions P_(M), and a contract force error between desired contactforce F_(D) F_(C) and an expected contact force F_(E).

Specifically, motor controller 36 (FIG. 5) of robotic actuator 40continually communicates sensed motor positions P_(S) and sensed motorcurrents I_(S) during respective stages S126 and S128 of scheme 120 tocontroller 24. In response thereto, controller 24 periodically measuressensed motor positions P_(S) and compares the measured motor positionsP_(M) to motor positions associated with a desired actuation positionP_(D) of the head of TEE probe 14 and the resulting position error is aninput for position control stage S122 designed to minimize the positionerror. In practice, controller 24 may execute any control technique(s)as known in the art for minimizing the position error (e.g., a PIDcontrol).

Controller 24 also periodically in sync measures sensed motor currentsI_(S) and combines the measured sensed motor currents I_(S) to anexpected motor currents I_(E), which is calculated by inputting measuredmotor positions P_(M) into the lookup table of stage S130 as generatedby calibrator 22 (FIG. 11). The lookup table takes two inputs ofposition of the two dials and returns two (2) expected current valuesI_(E) for each degree-of-freedom. During stage S132, expected currentvalues I_(E) and the measured motor current values I_(M) are current fedto force curve (C→F) computed by calibrator 23 (FIG. 12) to estimate anexpected contact force F_(E) on the head of TEE probe 14.

Force control stage S124 receives contact force correction F_(C) from acomparison of desired contact force F_(D) and expected contract forceF_(E) and adjusts a path generated by position control stage S122 tolimit the forces exerted by the head of TEE probe 14. In one embodiment,a direct method to model this motion is to assume that contact surfaceacts as an ideal spring, in which case:Δf=K(x−xo)

where Δf is the force error signal, x is the position of the contactpoint, xo would be the position of TEE probe 14 if there was noobstacle, and K is elastic constant of the esophagus of the patient(values known in literature can be used). Since x₀ can be known from thekinematic model of TEE probe 14, there is a direct link between motorcommands and the force. Similarly to position control value:

$x = {\frac{\Delta\; f}{K} + {x\; 0}}$

Controller 24 will continually loop through the stages of scheme 120during the procedure.

Referring to FIGS. 2-13, those having ordinary skill in the art willappreciate numerous benefits of the present invention including, but notlimited to, a sensorless force control for any procedure involving acable driven interventional tool (e.g., a TEE probe, a steerablecatheter, a guidewire, a colonoscope, etc.).

While various embodiments of the present invention have been illustratedand described, it will be understood by those skilled in the art thatthe embodiments of the present invention as described herein areillustrative, and various changes and modifications may be made andequivalents may be substituted for elements thereof without departingfrom the true scope of the present invention. In addition, manymodifications may be made to adapt the teachings of the presentinvention without departing from its central scope. Therefore, it isintended that the present invention not be limited to the particularembodiments disclosed as the best mode contemplated for carrying out thepresent invention, but that the present invention includes allembodiments falling within the scope of the appended claims.

The invention claimed is:
 1. A robotic actuation system for sensorlessforce control of an interventional tool having cable driven distal end,the robotic actuation system comprising: a robotic actuator operable tocontrol the interventional tool over a range of actuation positions,wherein the robotic actuator includes at least one motorized gearoperable to operate the cable drive of the interventional tool; and arobotic workstation operably connected to the at least one motorizedgear to generate motor commands for simultaneous actuation position andcontact force control of the interventional tool, wherein the roboticworkstation is operable to generate the motor commands as a function ofan actuation position measurement and a motor current measurement of theat least one motorized gear for a desired actuation position of theinterventional tool.
 2. The robotic actuation system of claim 1, whereinthe robotic workstation generates a motor position error as a functionof a comparison of a measured motor position of each at least onemotorized gear to a desired motor position of each at least onemotorized gear associated with the desired actuation position of theinterventional tool.
 3. The robotic actuation system of claim 1, whereinthe robotic workstation generates a contact force error as a function ofa comparison of an expected motor current of the motorized gear to adesired motor current of the motorized gear.
 4. The robotic actuationsystem of claim 1, wherein the robotic workstation generates a motorposition error as a function of a comparison of a measured motorposition of each at least one motorized gear to a desired motor positionof each at least one motorized gear associated with the desiredactuation position of the interventional tool; wherein the roboticworkstation generates a contact force error as a function of acomparison of an expected motor current of the motorized gear to adesired motor current of the motorized gear; and wherein the motorcommands are generated by the robotic workstation to minimize the motorposition error and the force error.
 5. The robotic actuation system ofclaim 3, wherein the robotic workstation includes a calibration lookuptable of expected motor currents for a measured motor position of eachat least one motorized gear; wherein the robotic workstation includes acalibration curve including a force-to-motor current curve for theinterventional tool; and wherein the robotic workstation derives theexpected contact force of the interventional tool from the calibrationlookup table and the calibration curve.
 6. The robotic actuation systemof claim 5, wherein the robotic workstation inputs the measured motorposition of each at least one motorized gear into the calibration lookuptable to output at least one expected motor current.
 7. The roboticactuation system of claim 6, wherein the robotic workstation applies theat least one expected motor current and a measured motor current of eachat least one motorized gear to the calibration curve to output theexpected contact force of the interventional tool.
 8. The roboticactuation system of claim 1, wherein the interventional tool is one of acable driven group of interventional tools including a probe, asteerable catheter, a guidewire and a colonoscope.
 9. The roboticactuation system of claim 1, wherein the robot actuator furtherincludes: a coupling of a handle base and a handle cover to define anactuation chamber for housing an engagement of the at least onemotorized gear to a handle of the interventional tool.